The present invention generally relates to information erasure by magnetic degaussing fields of effective strength and multi-dimensional direction applied to magnetic tapes and disks traversing a pathway. In particular, the invention relates to generating uniform magnetic field elements capable of generating and concentrating flux density fields.
Certain problems arise in arranging an array of simple magnetic poles that generate and rotate fields across a wide gap for purposes of degaussing both tapes rated above 1000 Oersteds with small form factors and half height hard disk drives rated above 1800 Oersteds. Arrangement of unlike poles closer to each other for purposes of increasing multidirectional strength of interacting fields increases interaction between poles on the same side of the gap, at the expense of strength midway across the gap, where worst-case generally resides. Especially in the situation with hard disk drives, where the information-bearing coatings are now rising past xe2x80x9chardxe2x80x9d coercivities of 3000 Oersteds, the non-uniform strength increases problems of extraction due to attraction between degaussing magnets and xe2x80x9csoftxe2x80x9d ferromagnetic motors of the drives.
The prior art of cladding electric windings with iron cores or surrounding cores with windings to produce pairs of like-poles facing each other across a gap can project uniform field strength due to typical construction features. Namely, electric current in winding portions beyond the ends of the iron cores can compensate almost perfectly for the fringing effects otherwise expected there. Replacing the electromagnet with permanent magnet materials constituting a pair of extruded xe2x80x9cExe2x80x9d, xe2x80x9cUxe2x80x9d, or horseshoe shapes forming like-poles facing each other across a gap does not counter the fringing effects. Increasing the length of the extrusion somewhat beyond media dimensions can provide some compensation. This approach faces difficulties in a case where two such extruded magnet pairs are to be arranged at 90 degrees to each other and at 45 degrees to a media path for purposes of exposing the circularly-oriented media to a variety of magnetic field directions in a single pass.
Problems in fabrication or assembly also arise in the application of extruded permanent magnet shapes to large degaussing gaps. Namely, permanent magnet elements sized to the poles can be fabricated and magnetized in one piece, or they can be fabricated and magnetized in smaller pieces to be attached together into an extruded shape. One-piece fabrication for high coercivity, wide gap degaussing involves dies and magnetizing sources and fixtures of inordinate size. Extreme repulsive force impedes assembly of large magnets from smaller elements.
U.S. Pat. No. 5,666,413 issued Sep. 9, 1997 to Kempf for xe2x80x9cScrambler Of Information Stored On Magnetic Memory Mediaxe2x80x9d specifies application of a single permanent magnet element for erasing thin magnetic storage media such as computer diskettes or floppy disks. U.S. Pat. No. 5,132,860 issued Jul. 21, 1992 to Von Stein for xe2x80x9cMagnetic Media Erasure Systemxe2x80x9d reveals various forms of permanent magnets, including complex shapes, extruded forms having like poles facing, and arrays intended to diminish magnetic strength upon passage of media.
This invention generally relates to information erasure by magnetic degaussing fields of effective strength and multi-dimensional direction applied to magnetic tapes and disks traversing a pathway. This invention particularly addresses erasure of small form factors having high coercivity, whether relatively thin or much thicker, within a single device without need for adjustment or reconfiguration. The invention may be configured for multiple-pass operation, requiring some operator skill and understanding of correct media manipulation, or for single-pass operation with effective improvements over prior art.
This invention relates to generation of single uniform fields, and to non-interacting systems of such fields, through the application of arrays of magnetic poles having simple geometry. Specifically, the arrays address problems of magnetic field uniformity arising from prior art application of extruded magnet shapes. Additionally, the arrays involve smaller elements than would be needed for extrusions, relieving difficulties in fabrication or assembly.
The strong, uniform magnetic fields generated by arrays of permanent magnet poles can be applied to degaussing wide ranges of magnetic media used to store information in various manners. For example, two non-interacting pole arrays can implement the familiar arrangement of fields at 90 degrees to each other and at 45 degrees to a media pathway, causing exposure to strength and range of direction with a single passage of media through that pathway. In applications sensitive to size, cost and weight that allow some operator skill and additional process time, a single array can be deployed with optimum performance achieved through multiple-pass technique. The media passing therethrough is uniformly exposed to the magnetic fields provided.